Week 4 - 2D Meshing for Sheet Metal

OBECTIVE

The objective of this assignment is to mesh the given CAD model with a target element length of 5 following the given quality criteria.

Sl no	Quality criteria	Value
1	Target /average length	5
2	Minimum length	3
3	Maximum length	7
4	Aspect	3
5	Warpage	15
6	Skewness	45
7	Jacobian	0.7
8	Minimum quad angle	45
9	Maximum quad angle	135
10	Minimum tria angle	30
11	Maximum tria angle	120
12	Tria percentage	15

The cad model image of the given assembly is shown below.

PROCEDURE

The model is imported onto ansa and then topology operation is performed. While doing topology it is made sure that components with different part IDs are not pasted together by selecting the appropriate option from the options list of topology tool as shown below.

Then it is checked for any geometry errors using the checks>geometry tool. It is then fixed. After cleanup the midsurface is generated using midsurface>skin option. While generating midsurface ,thickness can be applied to it automactically by selecting the "apply estimated thickness" options from the options list. After generating midsurface it is checked for any geometry issues. Then the components are meshed one by one.

The mesh parameters and mesh quality criteria is then assigned. Since our target element length is 5 , shell element length is set to 5 using length option (mesh>perimeters>length). Unwanted feature lines are suppresed using join (mesh>macros>join) tool. The component is then meshed part by part using mesh generation>best tool. The generated mesh may not always be good in quality so to improve quality shellmesh>reconstruct option is used when needed. Some of the common criterias that were followed to obtain a geat quality mesh were

• The tria elements should never be opposite to each other
• No tria elements should be connected back to back
• No tria elements should be on the edge of the geometry
• No tria elements should be on the edge of the geometry
• No tria elements should be near the holes.
• No tria elements should be on the feature and the fillets
• There should be less tria concentration.

Most quality issues relating to tria were managed using elements>split, elements>swap, elements>join, grids>paste ,shell mesh>smooth options.Warpage issues were common occourence in areas where there was a sharp turn in geometry, these were fixed by using grids>move tool . Sometimes shell mesh>smooth tool also worked.Some other tools which were used during meshing were macros>edge to perimeter, grids>origin ,mesh generation>erase, macros>cut etc.. Move hole option (mesh>grids>mv hole) was also utilised in this to enlarge holes so as to fix quality issues. Some components had symmetry , in such cases only half portion was meshed and the other half was reflected. For easy reflection of meshes working plane (topo>auxiliary>working plane) was extensively used.

RESULTS

The component was successfully meshed satisfying all the quality criterias .The final meshed model is shown below.